This invention relates to the formation of a Self-twist fibrous structure from two or more strands of similar count.
In British Pat. No. 1,015,291 is disclosed a method of forming what has become known as a self-twist yarn by the introduction into one or both of two strands alternating zones of opposite twist along the length of the strands and then converging the strands so that the or each twisted strand partly untwists around the other strand to form a stable self-twisted fibrous structure having alternate zones of opposite ply twist with some strand twist remaining in the or each twisted strand. This method may be applied either to two strands of similar count wherein generally both strands are twisted or to such a strand in combination with a much finer filament strand in which case only the coarse strand is twisted since twisting of the filament strand makes effectively no alteration to the structure of the finalised yarn.
The present invention is concerned only with the formation of a self-twist structure from strands of similar count and in this context "similar" means strands having counts such that when both are twisted the twist of each contributes effectively to the resultant structure. The invention can also be applied to structures having more than two strands particularly three-fold structures.
Since the development of self-twist structures in 1961 when the above patent was filed and during the time that these structures have been commercially used, that is since approximately 1969, it has always been accepted that when two strands of similar count are twisted and allowed to converge they will assume a natural balance of ply twist to remaining strand twist in the resultant self-twist structure and that this natural balance is unalterable. Clearly the natural balance is dependent upon the type of fibres employed, the coarseness of the strand and other factors in this complex twisting arrangement but it has always been held that such a balance or ratio is a natural and fundamental property of the strands and can either be calculated or determined by experiment and will be repeatable in all reconstructions of the twisted structure from the same strands or strands having the same properties.
It has been appreciated that this natural balance can in some circumstances and particularly with coarser yarns cause severe difficulties in that the remaining strand twist may be too high for a particular required ply twist thus causing the strands to appear very lean and rendering them totally unsatisfactory for commerical use.